La variabilidad de la frecuencia cardíaca como indicador del sistema nervioso autónomoefecto del ejercicio físico en adultos

Abstract

Background: Heart Rate Variability (HRV) describes differences between successive heartbeats. HRV reflects cardiac adaptability and the autonomic nervous system status. Higher HRV has been related to reduced stress levels and increased life expectancy, while a decreased HRV is usually associated with superior rates of morbidity and mortality. Previous studies have reported that physical exercise affects HRV. Nevertheless, it is currently unknown whether different physical exercise methodologies similarly influence HRV or not. Hence, understanding HRV´s role as a health indicator and the effects of different training methodologies on their related parameters has scientific and clinical relevance. Aims and hypothesis: The principal aim of this Doctoral Thesis is to analyze the effect of different training programs on HRV in sedentary adults. We hypothesize that (i) physical exercise significantly will increase HRV in sedentary middleaged adults, especially in those training programs based on high intensity intervals; and that (ii) HRV will be improved in young adults after the HIIT intervention independently of the daily ingestion of a moderate dose of alcohol. Material and methods: 156 adults (74 women) participated in this study. Participants were: (i) middle-aged adults (45–65 years old) from the FIT-AGEING research project; or (ii) young adults (18–40 years old) from the BEER-HIIT study. Participants from the FIT-AGEING study were randomly assigned to 4 groups: (a) a control group (no exercise), (b) a PAR group, (c) a HIIT group, and (d) a HIIT + EMS group. Participants from the BEER-HIIT study were allocated to different intervention groups that completed a HIIT training program combined with a daily but moderate dose of alcohol. HRV was measured before and after each intervention in resting conditions. HRV was recorded with Polar RS800CX and analyzed with the software HRV Kubios ®. SS (i.e., a sympathetic related HRV outcome) and S/PS Ratio (i.e., an autonomic balance index) were calculated and validated, obtaining reference values for both variables in adults through acceptance intervals. Results: Increases in vagal-related HRV parameters and decrements in HRV parameters related to sympathetic activity were observed in all training groups in middle-aged adults (all p<0.001). Moreover, exercise-induced changes were related to changes in body composition (i.e., lean mass index, fat mass index, and visceral adipose tissue) and cardiometabolic risk (all p<0.034). No changes were observed in HRV parameters in young adults after the intervention program (all p>0.380). Conclusion: The results from this doctoral thesis suggest the relevance of physical exercise aiming to improve HRV in middle-aged adults. These enhancements are directly related to exercise-induced changes in other healthrelated markers (i.e., body composition and cardiometabolic risk). Nevertheless, a 10-week HIIT intervention based on weight-bearing exercises in a circuit form did not have a significant impact on HRV parameters in healthy young adults.